1. Field of the Invention
The invention relates to a head protection airbag device having a configuration including an airbag which is folded and housed by the upper edge of a window in the vehicle interior side, which is fixed to the vehicle body at its upper edge, and which deploys and inflates so as to cover the vehicle interior side of the window while projecting downward from its housed position by allowing inflation gas from an inflator to flow therein.
2. Description of the Related Art
Conventionally, a head protection airbag device is like the one shown in JP-A-2003-54347. In the conventional head protection airbag device, an airbag includes an inflating portion inflating by allowing inflation gas to flow therein and a non-inflating portion into which inflation gas does not flow. In the conventional device, the area of the airbag which covers the vehicle interior side of the window when inflation is completed in the airbag includes the inflating portion and the non-inflating portion. This is for inhibiting the capacity of the airbag from increasing as much as possible while still securing protection of a passenger's head. Specifically, in the conventional head protection airbag device, the area of the airbag which covers the vehicle interior side when inflation is completed includes a head protection portion which is the inflating portion and a blocking portion which is the non-inflating portion. The head protection portion is a portion provided at the side of a seat, inflating by allowing inflation gas to flow therein so as to protect the passenger's head. The blocking portion is a portion which covers the vehicle interior side of the window, having a configuration in which inflation gas does not flow therein. Moreover, in the conventional head protection airbag device, a tension belt which is separated from the airbag is arranged at the portion of the blocking portion, this tension belt generating tension along the front-rear direction at the lower edge side of the airbag when inflation is completed. This is for preventing the passenger's head from moving greatly downward to under the lower edge of the blocking portion even when the passenger's head moves towards the vehicle exterior side as well as moving downward while abutting on the blocking portion.
However, in the conventional head protection airbag device, through the airbag has a configuration such that in completing inflation it generates tension along the front-rear direction at the lower edge side, but such that the area of the blocking portion formed by the non-inflating portion is thinner than the head protection portion which inflates by allowing inflation gas to flow therein. Therefore, when the airbag completes the inflation in a state in which a large tension is not generated at the lower edge side, the lower edge of the blocking portion tends to get closer to the window than the lower edge of the head protection potion. Also, the lower edge of the blocking portion easily climbs over the lower edge of the window. As a result, it is difficult for the conventional head protection airbag device to reliably prevent movement of the head of the passenger in the downward direction when the head abuts on the inflated airbag. In the conventional head protection airbag device, a tension belt which is separate from the airbag is inserted through a center portion of the blocking portion, the respective ends of the tension belt being connected to the vehicle interior side and the vehicle exterior side of the blocking portion. Therefore, if the head of the passenger abuts on the tension belt from above while abutting on the blocking portion of the airbag at the completion of inflation, the tension belt greatly departs from the blocking portion, pulling the portion arranged at the vehicle exterior side into the vehicle interior side. As a result, in the conventional head protection airbag device, it is difficult for the head to catch smoothly on the tension belt, and there is room for improvement of this device, to reliably prevent the downward movement of the passenger's head.